1. Field of the Invention
The invention relates to a wet-processing apparatus and a method of fabricating a display panel.
2. Description of the Related Art
A process of fabricating a display panel such as a plasma display panel (hereinafter, referred to as “PDP”) includes a step of forming various patterns on a substrate, such as an patterns of an electrode, a rib, a fluorophor layer, a black matrix, a black stripe, and a color filter.
For instance, a wet step in which a processing solution such as developing agent is used is usually applied to a step of forming patterns on a substrate.
Specifically, for instance, photosensitive material (photoresist) is coated in a pre-step all over a substrate by printing, seating or coating. Then, the sensitive material is exposed to light in a predetermined pattern. Then, the substrate is soaked into developing agent in a wet-processing bath, or developing agent is sprayed onto the substrate, to thereby remove a portion of the sensitive material which was not exposed to light (or exposed to light). Thus, the sensitive material is patterned on the substrate.
Consequently, a processing solution such as developing agent having been used for a wet step contains a material of which a pattern formed on a substrate is composed.
A used processing solution is usually used for a wet-step a plurality of times.
Since a material of which a pattern is composed (hereinafter, referred to as “pattern material”) is often expensive (for instance, Ag (silver) used for fabricating an electrode), it is preferable to separate and recover such pattern material out of a used processing solution for recycling.
For instance, the patent reference 1 suggests a process of separating and recovering pattern material out of a used processing solution by means of a filter, and recycling the processing solution out of which the pattern material was separated, to a wet step again (hereinafter, this process is referred to as “filter process”).
The patent reference 2 suggests a method of recycling phosphor contained in developing agent, including a step of (a) recovering the phosphor by still standing the developing agent to precipitate the phosphor, (b) recovering the phosphor by filtrating the developing agent, or (c) recovering the phosphor through the use of a centrifugal separator.
The patent reference 3 suggests a process of separating and recovering pattern material out of developing agent through the use of a decanter type centrifugal separator (hereinafter, this process is referred to as “centrifugal separator process”).    Patent reference 1: Japanese Patent Application Publication No. 10-242047    Patent reference 2: Japanese Patent Application Publication No. 11-228950    Patent reference 3: Japanese Patent No. 319772
The filter process suggested in the patent reference 1 is accompanied with a problem of high frequency of exchanging a filter. Furthermore, each time a filter is exchanged, it may be necessary to temporarily stop a production line. Accordingly, the filter process is not suitable to fabrication of a lot of large-sized substrates.
The process of recovering phosphor by filtrating developing agent, suggested in the patent reference 2, is accompanied with a problem identical with the above-mentioned problem.
Furthermore, the process of still standing developing agent to precipitate phosphor, suggested in the patent reference 2, is accompanied with a problem that it takes much time to separate and recover phosphor out of developing agent.
The centrifugal separator process as suggested in the patent references 2 and 3 is accompanied with a problem that a recover rate is relatively high in the case that pattern material contained in a solution has a high specific weight, whereas if the solution had a low specific weight, a recover rate would be lowered.
Specifically, for instance, in the case of fabricating a silver electrode having a high specific weight among materials to be used in a step of carrying out a wet step to form a pattern for PDP, there could be obtained a recover rate of 90% or greater. In contrast, in a process in which pigment material having a relatively low specific weight is used (for instance, a step of fabricating a black matrix), a recovery rate would be extremely lowered, specifically, lowered down to about 20%. Thus, the centrifugal separator process is accompanied with a problem that a recovery rate is much changed in dependence on a specific weight of pattern material (that is, impurities to be recovered out of developing agent).
In addition, when recycled developing agent out of which pattern material has been already separated is reused, if the recycled developing agent contains much impurities, there would be caused a problem, because of a low recovery rate of pattern material, that development quality is harmfully influenced, and thus, it would be impossible to stably form a pattern.
Furthermore, when recycled developing agent out of which pattern material has been already separated is reused, if the recycled developing agent contains much impurities, there would be caused a problem that conduits in which developing agent is circulated is clogged, and a nozzle through which developing agent is sprayed is clogged.
As a result, it is necessary in the centrifugal separator process to frequently exchange developing agent into new one in order to make it possible to stably form a pattern, and to avoid a path through which recycled developing agent is circulated, such as conduits and a nozzle, from being clogged.